Thermo-oxidation engine oil simulation testing

ABSTRACT

A method for testing engine lubricating oil under simulated engine operating conditions including a tank with an interior space containing a quantity of engine lubricating oil, an elongated tubular enclosure for passing oil from one end to the other, and an oil pump to cause oil to flow from the tank through the tubular enclosure. The tank includes devices to introduce oil oxidizing agents to the oil. A metal rod extends centrally through the enclosure so that oil passes along its outer surface and the rod is selectively heated so that oxidation deposits form along the rod. Examination and analysis of the rod and its deposits permit rating of a particular oil for its oxidation resistant properties.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a division of application Ser. No. 08/074,529, filedJun. 11, 1993, now U.S. Pat. No. 5,287,731, by the same inventors as inthe present application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The subject invention relates to an apparatus and a method for testingoxidation resistant properties of lubricating oils for internalcombustion engines and particularly turbocharged internal combustionengines. In a normal engine, the oil is exposed to relatively hightemperatures and containments which can induce oxidation of the oil. Aturbocharged engine, in addition, exposes the oil to the very hightemperatures of the turbocharger shaft. When a hot engine is shut-off,the temperature of the turbocharger increases dramatically. Oilcontacting very hot portions of the turbocharger can be rapidly oxidizedand produce undesirable deposits on the internal metal surfaces. It canbe understood that it is desirable to test oil under conditionssimulating a hot engine.

The subject apparatus and method evaluates the oxidation resistentqualities of various oils under simulated engine and turbochargerconditions. The apparatus includes a reservoir holding a quantity of oilwhich is heated and exposed to contain such as moist air and nitrousoxide. These contaminants can cause formation of certain partiallyoxidized precursors which in turn can lead to deposit formation. The oilis pumped from the reservoir to a depositor apparatus which includes aheated rod over which the oil flows. Contact between the oil and theheated rod simulates the contact of hot oil with a turbocharger shaft ofan engine. The temperature of the heated rod varies along its length dueto the cooling effect of oil flowing along and over thereof. Deposits ofoxidized products are formed on the surface of the rod and the quantityof the deposit can be determined by a differential weight method. Alsothe appearance of the deposits can be studied to evaluate the oxidationresistance of lubricating oils.

2. Description of Related Art

There are several tests which are commonly conducted on lubricating oilto determine the oxidation effects of heating the oil. Equipment isavailable to perform infra-red spectra analysis on lubricating oils todetect various oxidation products. Other equipment is available to do ametals analysis or content on the oil. Neither of these tests veryaccurately reflects the environment of a hot engine and particularly aturbocharged engine.

It is known to test lubricating oil by passing lubricating oil over aheated rod. To a degree, this simulates an engine environment. However,it does not provide the two-stage thermal/oxidation effects of thesubject apparatus and method. First, the subject apparatus and methoduses an oil reservoir simulate to oil in an engine oil pan. The oil inthe reservoir is heated and exposed to containments such as moist airand other oxidizing agents such as nitrous oxide. Secondly thecontaminated oil is passed over a heated rod to stress the oil whichtends to produce oxidation deposits on the rod. Applicant knows of noother test apparatus and method which provides such a two-stage thermaloxidation for lubricating oil as explained in more detail hereinafter.

SUMMARY OF THE INVENTION

The subject apparatus and method evaluates the oxidation resistentqualities of various oils and is particularly well suited for evaluatingengine lubricating oils. The oil in an engine pan is exposed torelatively high temperatures and also to containments which tend tooxidize the oil particularly at higher temperatures. Moisture andvarious byproducts of gasoline enter the crank case of an engine and mixwith the oil. It is known that these conditions in the oil pan tend toform certain partially oxidized products which are procures to formationof deposits particularly on hot surfaces of the engine. The shaft of theturbocharger is one of the hotter surfaces to which oil is applied. Theengine's oil pan acts on the oil and carries out a reaction stage. Whenthe partially oxidized oil from the pan is pumped to a hot area of theengine such as the shaft of the turbocharger, these partially oxidizedproducts or procurers further oxidize and form deposits on the hotmetal. The deposits resemble varnish, hardened sludge or ashen appearingsubstances.

It is desirable to evaluate oils of the basis of their oxidationresistent qualities under engine-like conditions. The subject apparatusand method permits evaluation by simulating the atmosphere andconditions of an engine for lubricating oil. The reservoir simulates theengine oil pour. The oil is further pumped to a hot component tosimulate a turbocharger for example. The apparatus includes a heated rodover which oil flows and on which oxidized products of the oil aredeposited. The quantity of these deposits can be determined by adifferential weighing process (weighing before and after the test). Thetemperature along the rod varies depending on the distance from the oilinlet. Much can be learned about the oils oxidization resistentqualities by the appearance and position of the deposit on the heatedrod. Varnishes, hardened sludges and ashen appearing deposits are formedalong the rod. Thus the range of deposits on the rod presents a kind ofthermal-gram of the different temperatures encountered by the oil alongthe rod.

It has been found that the subject apparatus and method for evaluatingoils for their oxidation resistent qualities is repeatable from test totest. Further, the apparatus and method is suited to the addition ofother test methods such as infra-red spectra analysis or a metalsanalysis.

Further advantages of the subject apparatus and method will be moreapparent by reference to the following detailed description of anembodiment, reference being to the drawings hereof of a preferredembodiment,

IN THE DRAWINGS

FIG. 1 is a somewhat schematic elevational and section view of the testapparatus; and

FIG. 2 is an enlarged and sectioned view of a deposit formation assemblyof the test apparatus shown in FIG. 1.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

In FIG. 1, the test apparatus or engine simulation oil testing apparatus10 is shown. Apparatus 10 includes a reactor vessel or enclosure 12having interior space 14. A quantity of lubricating oil 16 partiallyfills space 14. A combination heater and insulating mantle 17 encirclesthe reactor vessel 12 to maintain the temperature of the oil 16 at adesired level corresponding to a typical oil temperature in an internalcombustion engine, typically above 95 degrees centigrade.

The reactor enclosure 12 has an outlet passage 18 near its bottomportion for withdrawal of oil from interior 14. A conduit 20 connectsoutlet 18 to the inlet of a pump 22. A conduit 24 connects the outlet ofpump 22 to a three-way fitting 26 having an inlet and two outlets. Oneof the outlets is connected by a conduit 28 to another fitting 30 whichextends through the upper wall of the reactor enclosure 12 and serves asan inlet for the return of oil into space 14.

The other outlet of connector 26 is connected to a micro-meter valve 34by a connector 36. The valve 34 in turn is connected by a conduit 38 toan inlet passage 40 leading to the interior 42 of a depositor assembly44. The depositor assembly 44 has an outer cylindrical member 46 withupper and lower threaded end fittings 48 which removably attach thereto.A tubular metal rod 50 extends through the interior 42 and also throughthe end fittings 48. An annular passage is formed between the outercylinder 46 and the rod 50 through which oil is pumped. An outletpassage 52 is formed at the upper end of the depositor assembly 44. Atthe upper end of assembly 44, a passage 52 is connected by conduit 54 toa filter 56. In turn, filter 56 is connected by a conduit 58 to theinlet fitting 30 to interior space 14.

The interior 14 of the reactor vessel 12 is vented by conduit 60 whichdefines a passage 62. An inlet is located passage 64 at the bottomportion of the reactor enclosure 12 to introduce containments such asmoist air or nitrous oxide to the oil 16. The containments flow to inlet64 through a passage 66 which is connected to a fitting 68. Fitting 68has an inlet 70 connected to passage 66 and inlets 72, 74 connectedrespectively to a source of moist air and to a source of nitrous oxide.Further, a valved drain passage 76 is provided so that the contents 16of the enclosure 12 can be drained.

FIG. 2, illustrates details of the depositor assembly 44. Metal rod 50has an outer cylindrical surface 80 located between inlet 40 and outlet52. Pump 22 causes oil to flow over and along rod surface 80 at a ratedetermined by the micro-meter valve 34. The valve 34 allows the pump tooperate at full capacity and bypasses most of the oil into conduit 28and back to the interior 14 in bypass relation to the depositor assembly44. During a test, the metal tube 50 is heated by electrical induction.This temperature is reflected within interior 82 of the tube 50. An oilinlet thermalcouple 84 is placed within the interior 82. Electricalleads 86 extend out from the lower end of the tube 50. Anotherthermalcouple 88 is positioned upward from thermalcouple 84 and hasleads 90 which extend from the upper end of the tube 50. The differencebetween the thermalcouple outputs is used by an associated control andsoftware program to control the temperature of the rod at a desiredlevel. Thermal couple 88 also acts as a maximum temperature control toshut-off the electrical induction heating when portions of the rodexceed a maximum temperature.

The outer surface 80 of the rod 50 and in particular the upper surface94 tends to receive formations of oxidized oil product or carbonyls. Thethickness of these deposits build up as indicated by numeral 92. Thedeposit formation 92 insulates the portion of the rod thereunder fromthe cooling affect of oil flowing thereby and eventually that portion ofthe rod exceeds the maximum temperature allowed by thermal couple 88. Atthat time, the thermal couple 88 signals the associated control toterminate heating of rod 50 and thus signals the end of the test.

At the end of the test, the oxidized oil in interior 14 can be drainedthrough valved drain passage 76. The filter 56 can be removed andexamined for particles of oxidized products which were not deposited onthe rod 50. In addition, the end caps 48 are removed from the cylinder46 and the rod 50 carefully removed from the interior 42. The rod isthen accurately weighed and the extent of the deposit 92 is determinedby subtracting the pre-test weight of the rod. Also, the appearance ofthe deposits 92 reveals a variation of varnish, hardened sludge andashen appearing deposits along its length with the ashen depositsappearing closer to the outlet passage 52 where the temperature of therod is greatest.

TEST PARAMETERS

As previously mentioned, the reactor enclosure 12 simulates the oil panand interior of an internal combustion engine in which a quantity oflubricating oil 16 is heated and exposed to various contaminants such asmoist air and oxidizing gases from the fuel and products of combustion.These fuel related contaminants act as oxidizing agents and have thesame affect on oil as does nitrous oxide. The oil 16 in the enclosure 12is heated by an insulated mantle 17 to a temperature simulating thetemperature of oil when operating engine, such as 95 degrees centigrade.The pump 22 withdraws some of the oil and pumps a portion of it into thedepositor assembly 44.

The heating of rod 50 is cycled to simulate the conditions of aturbocharger when an engine is operating and when a hot engine isdeactivated. Upon deactivation, the temperatures of the engine andturbocharger increase substantially and this is the worst condition towhich oil is exposed.

A typical test uses about 100 millimeters of oil in the reactorenclosure. The valve 34 controls the flow rate of oil through thedepositor assembly 44 at 0.46 millimeters per minute. Moist air andnitrous oxide are introduced into interior 14 at a rate of 20 ccs perminute. The temperature of lubricating oil in the reactor is maintainedat 95 degrees centigrade. A typical heating cycle for the rod 50 is asfollows: First, the rod is heated to 150 degrees centigrade and held atthat temperature for one minute. The rod is then increased intemperature to 500 degrees centigrade and held at 500 degrees centigradefor two minutes. The rod is then decreased in temperature to 150 degreescentigrade and held at that temperature for 24 minutes. The entire cycletakes 30 minutes. The cycle is repeated many times.

At the end of the test, the oil is drained from interior 14 andanalyzed. The rod 50 is removed and weighed to determine the depositquantity. The rod is also visually analyzed to determine depositquality. In addition, materials collected by the filter can be studiedand/or weighed.

Although one embodiment of apparatus for oil testing is shown anddescribed for performing a specific testing method, it is contemplatedthat there may be modifications which still fall within the inventivescope as defined by the claims.

What is claimed is as follows:
 1. For determining the relative oxidationresistances of different engine lubricating oils, the method ofsimulating the treatment of oil in an internal combustion engine,comprising the steps of:providing a reactor enclosure for deposit of aquantity of heated oil; introducing the heated oil into the reactorenclosure; introducing oxidizing agents to the quantity of heated oilwhereby partially formed oxidation products are formed; passing theheated oil and its partially oxidized products over the surface of aheated metal rod; observing and measuring the deposits on the heatedmetal rod by the weight difference between the heated metal rod beforeand after the simulation.
 2. The method as set forth in claim 1 andfurther comprising the steps of:filtering oxidized products suspended inthe flow of heated oil and not deposited on the heated metal rod;determining the filtered products by observation and the weightdifference between the filter before and after the simulation.